Hi, First posting so please be gentle! So a bit of history. Last year I had a problem with my radiators not heating up, well, only getting tepid. Hot water was fine, and having the hot water on helped get slightly more heat in the radiators. I decided it was the 3 port valve, so replaced the synchron motor and it did seem to make a big difference, in that all radiators got to something approaching hot. Anyway, BG came round the other day for a first visit / boiler service as part of my new homecare contract. The engineer noted that although the boiler gets hot in no time, no heat was going into the radiators again, which was odd as it was doing before he started. He advised that there was a blockage in the system somewhere. Sure enough none of the radiators upstairs or downstairs are getting much heat. Upstairs ones are warmer than the downstairs ones though, which are barely tepid. Apart from one radiator. Which is a new towel radiator I installed last week as part of an en-suite bathroom install. This one is piping hot! Bled the rads and no air has come out. Noted for a couple of months now that the pump is noisy, and sometimes if you listen to it closely it makes a kind of fizzing noise as though small amounts of air are passing through. Went to check the 3 port valve the other night, just wondering if there was something up with that again. Noted that the BG engineer had left it switched to manual, put it back to auto. The lever is loose regardless of whether CH or HW are on. Only way it returns against spring pressure is if all the power is turned off. I'm wondering whether there is a blockage or an air lock or even the pump is failing. I've tipped some Sentinel X400 into it with the intention of leaving it a week or so, then draining down. System details are: Worcester Greenstar 29 HE boiler in kitchen, combined cylinder and header tank upstairs, fitted with Honeywell 3 port valve and Grundfos pump. Majority of the house is plumbed with 10mm speedfit. System (and house) is 15 years old. Appreciate any ideas folks may have, thanks!